Look on your desktop. Do you see a folder called; Old Firefox? Look inside. Look for the folder with the latest creation date.

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

There's none. I have Ubuntu 18.04.2 LTS 64-bit. I searched through .mozilla folder. I have found only one bookmarks backup, apparently right after the upgrade, containing only the initial 5-or-something bookmarks that go with the program.

Slowly losing hope and cursing myself for not doing back-ups of bookmarks regularly. I did last ones in September.

September is better than nothing. How was the file saved/created?

Bookmarkbackups are automatically done every day that Firefox is used, and the default number of saved backups is 15. Hopefully the Ubuntu build of Firefox didn't change that default setting.

If all you have is - 1 backup - my guess is that you are using a new Profile.

Open about:profiles and see how many Profiles are listed.

FredMcD said

September is better than nothing. How was the file saved/created?

I did it manually, there's an option of creating a backup, it's JSON file. Except it ain't gonna help me, because I've started two projects in December and except for very few links that I sent through my personal email to my work email, it's gone.

___________________________________________________

the-edmeister said

Bookmarkbackups are automatically done every day that Firefox is used, and the default number of saved backups is 15. Hopefully the Ubuntu build of Firefox didn't change that default setting. If all you have is - 1 backup - my guess is that you are using a new Profile. Open about:profiles and see how many Profiles are listed.

Only one profile, the default one, is listed. When I open the directory and go up, there aren't any other folders concerning profiles. :(

Back up and restore information in Firefox profiles.{web link} I use an add-on that makes backups of my user profile, Just In Case. Unfortunately, it is not compatible with the current Firefox.

Every now and then, open the profile folder and create a copy of the current profile as is to another location on your hard drive. This way you will have a backup.

If you do this each day, you will not lose much data. This should be done with Firefox Closed.

Note: In case you need to restore from these backups, you may need to overwrite old or corrupted files.

Windows and Macs have a function that can restore the system to a prior time. Can Linux do this?

FredMcD said

Windows and Macs have a function that can restore the system to a prior time. Can Linux do this?

No, it can't. Unless you get an app such as TimeShift. I didn't have TimeShift, thus it can't save me.

Let's try to solve only how could the lost data be saved, because there's no way I'm trusting bookmarks again. (I'll most likely go fully to emailing links, then I have it with me everywhere and it's on both of my emails, so pretty much very easily accessible when I'm at work).

Now I'm trying to figure out if there is a way of undo update of Firefox. In my opinion, unless my dear backstabber PC hid it real well, the data are gone and even if I'd find a way to undo updates, it would most likely be lost. But it's worth a shot anyways. Any ideas?

Btw, thank you for the help you already gave me, it's much appreciated.

Wish I could be more help.

Note: Some versions of Quantum change how the data files are set up, so they are not backward compatible.